S-350 High Pitched Engine Squeal - PeachParts Mercedes-Benz Forum

oldsouth · #1 11-06-2007, 10:12 PM

I need a little feedback here. My '95 S350 has developed a high pitched metallic sounding squeal. It started about a year ago and was so high pitched I could not hear it. My wife and kids could hear it though. The last month or so, it has become much worse and I can acutally hear it now. The pitch is still high though and metallic sounding. I was so convinced that it was the turbo bearings or the turbo blades barely hitting the housing that I sent the turbo off to be rebuilt by Garrett. Well Garrett said they found nothing wrong with the turbo, but I had them go through it anyway since it was off. I put it back on and still have the squeal. The squeal only occurs at a certain RPM and load of the engine. Mainly at 70-80 mph. It will do it some accelerating when it gets into that same load condition. It will not squeal at full throttle. As a matter of fact, I ran the car full throttle for about 5 miles trying to see if anything would give or not. Not any squeal at all. I slowed down to 75 mph and it started squealing. I got it to squeal in my shop one time by reving it up to about 3500 rpm's and then going full throttle. It gave a squeal then. It is really loud and uncomfortable to cruise when this occurs. I usually just speed up until it quits. Car has 347,000 miles and uses about 1 quart every 1200 miles. Good power. Original engine. Had a valve job about 2 years ago. Nothing else. Anyone have any ideas of what to check?? I took the valve cover off today and let it idle and saw nothing out of the ordinary. I did not rev it up because it was slinging enough oil at idle to get it everywhere. I took an oil sample and should have the results on Wednesday. Maybe that will show something. Any ideas?

Hatterasguy · #2 11-06-2007, 10:21 PM

I'm trying to think what would make that noise. Sure its not the water pump, or another belt driven accessory? Vacuum pump maybe?

oldsouth · #3 11-06-2007, 10:32 PM

Vacuum pump is relatively new. I think I had the problem before changing the vacuum pump. I thought about the water pump, but how could you check that running 70-80 mph. I could remove the belt that turns it, but wouldn't it overheat quickly?

I just went and checked my service records and I do not think I have ever replaced the water pump. If I did, I did not write it down; and I write everything down. Could possibly be the bearing in the water pump?

Hatterasguy · #4 11-06-2007, 10:52 PM

Remove the belt and spin it with your hands, see how smooth the bearing feels. Mine made a high pitch whine at idle, and just off idle as it was dieing.

Is it RPM related? Whats 70-80, about 3k-3.5k?

oldsouth · #5 11-06-2007, 11:31 PM

70-80 = 2700-3000 rpms